Effects of supplementary feeding level on digestion and energy utilization by sheep and goats grazing arid-area rangelands

Abstract

An experiment was implemented to examine differences between sheep and goats in the utilization of open arid-area rangelands when provided with different concentrate supplement levels. Fifty-two non-lactating females (Abu-duleik sheep, n = 26 and Balady goats, n = 26) were employed in a 90-day experimental period. Animals of each species were allocated randomly into two treatments, according to a 2 × 2 factorial arrangement, with animal species (goats and sheep) and concentrate level (low and high) as main factors. They were grazing widely over the arid-area rangelands with a limited amount of a concentrate supplement, low (1 % BW) or high (2 % BW) (DM basis). Total energy expenditure was estimated by heart rate (HR) monitors for 48 h after its calibration by oxygen consumption with a face mask open-circuit respiratory system. However, the significant interaction between animal species and concentrate levels of supplement indicated that increasing the concentrate level had a negative effect (P < 0.05) on forage intake (22.8 vs. 17.0 ± 1.58 g/ kg BW, for goats supplemented with low or high concentrate level, respectively) and digestibility by grazing goats. The reduction in goat’s digestibility was mainly attributed to the reduction (P < 0.01) in fiber fraction digestibility (546 vs. 441 ± 24.0 g/ kg dry matter intake, respectively). The contrary was observed in sheep in which the greatest forage consumption and digestibility were observed in grazing sheep supplemented with a high concentrate level, including the fiber fraction digestibility. Total energy expenditure was similar between sheep and goats when supplemented with a low concentrate level (600 and 574 ± 24.6 kJ/ kgBW0.75, respectively), while it was significantly (P < 0.01) greater for sheep than for goats when supplemented with a high level (776 vs. 577 ± 24.6 kJ/ kg BW0.75, respectively). This was reflected in the energy balance (EB) that was negative and similar in sheep and goats at a low supplementation level (−55.2 and −64.3 ± 14.27 kJ/ kg BW0.75, respectively, while sheep reported positive (P < 0.05) and greater EB than that of goats with a high level (71.5 vs. 2.7 ± 14.27 kJ/ kg BW0.75, respectively). In conclusion, concentrate supplement is necessary to maintain animals without nutritional deterioration while grazing in the open arid-area rangelands, however, its effects on the ability to utilize a low quality forage differed between sheep and goats at a high supplementation level.